This invention relates to a methodology for etching microfabrication substrates.
In microfabrication, the problem often arises of etching through a stack that contains alumina, silver, and titanium. One possible fabrication technique is wet etching that combines HF (etches alumina), hydrogen peroxide (oxidizes Ag and Ti), and ammonia (dissolves AgO into an aqueous ionic solution.) Features approximately 10 microns in characteristic dimensions may be made using such a wet etching technique.
Using wet etching, however, to make smaller/narrower features may be problematic, because the etching tends to widen the feature until the tolerance is no longer maintained. Indeed, lateral etch rates may be almost 20× faster than the vertical etch rate through the stack. Wet etching may also etch much faster in small gaps than in wider areas, such that the final dimensions depend on the dimensions of the original feature. Agitation of the part may not affect these etch rates. It is possible that the etchant tracks along the alumina/silver interface, thus traveling laterally in the material while etching it.
Accordingly, the etching of small features in a microfabrication substrate remains an unresolved problem.